Arylsulfinate salts in photoinitiator systems for polymerization reactions

ABSTRACT

Compositions are provided that include an electron donor and a sensitizing compound. More specifically, the electron donor is an arylsulfinate salt. Methods of polymerization are also provided that can be used to prepare polymeric material from a photopolymerizable composition that includes ethylenically unsaturated monomers and a photoinitiator system. The photoinitiator system includes an electron donor and a sensitizing compound.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 11/380,028 filed 25Apr. 2006, now U.S. Pat. No. 7,541,389, which is a divisional of U.S.Ser. No. 10/847,523 filed 17 May 2004 and issued as U.S. Pat. No.7,064,152, which claims priority to U.S. Provisional Patent ApplicationNo. 60/506,396 filed on 26 Sep. 2003.

TECHNICAL FIELD

Arylsulfinate salts are provided that can be used as electron donors ininitiator systems for free radical polymerization reactions.

BACKGROUND

Free radical polymerization reactions typically have an initiatorsystem. In some applications, the initiator system is a photoinitiatorsystem that can be based on various chemical approaches. For example,free radical polymerization reactions can be initiated using athree-component photoinitiator system that includes an electronacceptor, an electron donor, and a sensitizing compound. Alternatively,an electron donor in combination with a sensitizing compound can be usedas a photoinitiator system.

In a three-component photoinitiator system that includes an electrondonor, electron acceptor and a sensitizing compound, there is typicallyno direct reaction between the electron donor and the electron acceptor.Rather, the sensitizing compound usually absorbs actinic radiationresulting in the formation of an excited sensitizing compound. Theelectron donor can donate an electron to the excited sensitizingcompound. That is, the sensitizing compound can reduced and the electrondonor is oxidized. The reduced sensitizing compound can be a radicalanion that can donate an electron to an electron acceptor to yield aninitiating free radical for the polymerization reaction. The initiatingfree radical can be the reduced electron acceptor. In some instances ofa three-component photoinitiator system, the oxidized electron donor canbe a radical species that also functions as an initiating free radical.

Other photoinitiator systems have a sensitizing compound and an electrondonor but no electron acceptor. The sensitizing compound can absorbactinic radiation to form an exited sensitizing compound. The electrondonor can donate an electron to the excited sensitizing compoundresulting in the oxidation of the electron donor. The oxidized electrondonor can be a radical species that functions as an initiating freeradical for polymerization reactions.

SUMMARY

Compositions are provided that include an electron donor and asensitizing compound. More specifically, the electron donor is anarylsulfinate salt. Methods of polymerization are also provided that canbe used to prepare polymeric material using a free radicalpolymerization reaction. The polymerization reaction is photoinitiatedwith a composition that includes an aryl sulfinate salt and asensitizing compound.

One aspect of the invention provides a composition that includes anelectron donor and a sensitizing compound capable of absorbing actinicradiation in the wavelength range of 250 to 1000 nanometers. Theelectron donor has an oxidation potential in N,N-dimethylformamide of0.0 to +0.4 volts versus a silver/silver nitrate reference electrode andincludes an arylsulfinate salt having an anion of Formula I

and having a cation containing at least one carbon atom and either apositively charged nitrogen atom or a positively charged phosphorusatom. The Ar¹ group in Formula I is a substituted phenyl, anunsubstituted or substituted C₇₋₃₀ aryl, or an unsubstituted orsubstituted C₃₋₃₀ heteroaryl. A substituted Ar¹ group can have asubstituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group. Thecomposition can further include ethylenically unsaturated monomers.

A second aspect of the invention provides a photopolymerization methodthat includes irradiating a photopolymerizable composition with actinicradiation until the photopolymerizable composition gels or hardens. Thephotopolymerizable composition includes an ethylenically unsaturatedmonomer, a sensitizing compound, and an electron donor. The sensitizingcompound is capable of absorbing a wavelength of actinic radiation inthe range of 250 to 1000 nanometers. The electron donor has an oxidationpotential in N,N-dimethylformamide of 0.0 to +0.4 volts versus asilver/silver nitrate reference electrode and includes an arylsulfinatesalt. The arylsulfinate salt has an anion of Formula I

and a cation that contains at least one carbon atom and either apositively charged nitrogen atom or a positively charged phosphorusatom. The Ar¹ group in Formula I is a substituted phenyl, anunsubstituted or substituted C₇₋₃₀ aryl, or an unsubstituted orsubstituted C₃₋₃₀ heteroaryl. A substituted Ar¹ group can have asubstituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group.

Another aspect of the invention provides arylsulfinate salts. In oneembodiment of the compounds, the arylsulfinate salt has an anion ofFormula I

where Ar¹ is a substituted phenyl, an unsubstituted or substituted C₇₋₃₀aryl, or an unsubstituted or substituted C₃₋₃₀ heteroaryl. A substitutedAr¹ group can have a substituent that is an electron withdrawing groupor an electron withdrawing group in combination with an electrondonating group. The cation of the arylsulfinate salt is of Formula II

where R¹ is an alkyl or aryl and each R⁴ is independently hydrogen,alkyl or aryl. The R¹ and R⁴ groups can be unsubstituted or substituted.An alkyl group can be substituted with a hydroxy. An aryl can besubstituted with a hydroxy, alkyl, or combinations thereof.

In another embodiment of the compounds, the arylsulfinate salt has ananion of Formula I

where Ar¹ is a substituted phenyl, an unsubstituted or substituted C₇₋₃₀aryl, or an unsubstituted or substituted C₃₋₃₀ heteroaryl. A substitutedAr¹ group can have a substituent that is an electron withdrawing groupor an electron withdrawing group in combination with an electrondonating group. The cation of the arylsulfinate salt is a ring structurethat includes a 4 to 12 member heterocyclic group with a positivelycharged nitrogen atom and at least one other heteroatom selected fromnitrogen, oxygen, sulfur, or combinations thereof. The heterocyclicgroup can be saturated or unsaturated. The cationic ring structure canbe unsubstituted or have a substituent selected from an alkyl, aryl,acyl, alkoxy, aryloxy, halo, mercapto, amino, hydroxy, azo, cyano,carboxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonyl group, orcombinations thereof.

In yet another embodiment of the compounds, the arylsulfinate salt hasan anion of Formula I

where Ar¹ is a substituted phenyl, an unsubstituted or substituted C₇₋₃₀aryl, or an unsubstituted or substituted C₃₋₃₀ heteroaryl. A substitutedAr¹ group can have a substituent that is an electron withdrawing groupor an electron withdrawing group in combination with an electrondonating group. The cation of the arylsulfinate salt is of Formula III

where each R² is independently an alkyl or aryl that is unsubstituted orsubstituted. An alkyl can be substituted with a hydroxy. An aryl can besubstituted with a hydroxy, alkyl, or combinations thereof.

The above summary is not intended to describe each disclosed embodimentor every implementation of the present invention. The detaileddescription section that follows more particularly exemplifies theseembodiments.

DETAILED DESCRIPTION

Compositions are provided that include an electron donor and asensitizing compound. More specifically, the electron donor is anarylsulfinate salt. Methods of polymerization are also provided that canbe used to prepare polymeric material from a photopolymerizablecomposition that includes ethylenically unsaturated monomers and aphotoinitiator system. The photoinitiator system includes an electrondonor and a sensitizing compound.

DEFINITIONS

As used herein, the terms “a”, “an”, and “the” are used interchangeablywith “at least one” to mean one or more of the elements being described.

As used herein, the term “actinic radiation” refers to electromagneticradiation capable of producing photochemical activity.

As used herein, the term “acyl” refers to a monovalent group of formula—(CO)R^(a) where R^(a) is an alkyl or aryl group.

As used herein, the term “alkenyl” refers to a monovalent radical of analkene (i.e., an alkene is an aliphatic compound having at least onecarbon-carbon double bond).

As used herein, the term “alkoxy” refers to a group of formula —OR whereR is an alkyl group. Examples include methoxy, ethoxy, propoxy, butoxy,and the like.

As used herein, the term “alkoxycarbonyl” refers to a monovalent groupof formula —(CO)OR where R is an alkyl group. An example isethoxycarbonyl.

As used herein, the term “alkoxysulfonyl” refers to a monovalent grouphaving the formula —SO₃R where R is an alkyl group.

As used herein, the term “alkyl” refers to a monovalent radical of analkane. The alkyl can be linear, branched, cyclic, or combinationsthereof and typically contains 1 to 30 carbon atoms. In someembodiments, the alkyl group contains 1 to 20, 1 to 14, 1 to 10, 4 to10, 4 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groupsinclude, but are not limited to methyl, ethyl, n-propyl, isopropyl,n-butyl, tert-butyl, isobutyl, n-pentyl, n-hexyl, cyclohexyl, n-octyl,n-heptyl, and ethylhexyl.

As used herein, the term “alkylsulfonyl” refers to a monovalent group offormula —SO₂R where R is an alkyl group.

As used herein, the term “alkynyl” refers to a monovalent radical of analkyne (i.e., an alkyne is an aliphatic compound having at least onecarbon-carbon triple bond).

As used herein, the term “amino” refers to a monovalent group of formula—NR^(b) ₂ where each R^(b) is independently a hydrogen, alkyl, or arylgroup. In a primary amino group, each R^(b) group is hydrogen. In asecondary amino group, one of the R^(b) groups is hydrogen and the otherR^(b) group is either an alkyl or aryl. In a tertiary amino group, bothof the R^(b) groups are an alkyl or aryl.

As used herein, the term “aminocarbonyl” refers to a monovalent group offormula —(CO)NR^(b) ₂ where each R^(b) is independently a hydrogen,alkyl, or aryl.

As used herein, the term “aromatic” refers to both carbocyclic aromaticcompounds or groups and heteroaromatic compounds or groups. Acarbocyclic aromatic compound is a compound that contains only carbonatoms in an aromatic ring structure. A heteroaromatic compound is acompound that contains at least one heteroatom selected from S, O, N, orcombinations thereof in an aromatic ring structure.

As used herein, the term “aryl” refers to a monovalent aromaticcarbocyclic radical. The aryl can have one aromatic ring or can includeup to 5 carbocyclic ring structures that are connected to or fused tothe aromatic ring. The other ring structures can be aromatic,non-aromatic, or combinations thereof. Examples of aryl groups include,but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl,acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl,perylenyl, and fluorenyl.

As used herein, the term “aryloxy” refers to a monovalent group offormula —OAr where Ar is an aryl group.

As used herein, the term “aryloxycarbonyl” refers to a monovalent groupof formula —(CO)OAr where Ar is an aryl group.

As used herein, the term “aryloxysulfonyl” refers to a monovalent grouphaving the formula —SO₃Ar where Ar is an aryl group.

As used herein, the term “azo” refers to a divalent group of formula—N═N—.

As used herein, the term “carbonyl” refers to a divalent group offormula —(CO)— where the carbon atom is connected to the oxygen atom bya double bond.

As used herein, the term “carboxy” refers to a monovalent group offormula —(CO)OH.

As used herein, the term “conjugated” refers to unsaturated compoundshaving at least two carbon-carbon double or triple bonds withalternating carbon-carbon single bonds and carbon-carbon double ortriple bonds.

As used herein, the term “cyano” refers to a group of formula —CN.

As used herein, the term “dialkylphosphonato” refers to a group offormula —(PO)(OR)₂ where R is an alkyl. The formula “(PO)” indicatesthat the phosphorus atom is bonded to an oxygen atom with a double bond.

As used herein, the term “diarylphosphonato” refers to a group offormula —(PO)(OAr)₂ where Ar is a aryl.

As used herein, the term “electron donating” refers to a substituentthat can donate electrons. Suitable examples include, but are notlimited to, a primary amino, secondary amino, tertiary amino, hydroxy,alkoxy, aryloxy, alkyl, or combinations thereof.

As used herein, the term “electron withdrawing” refers to a substituentthat can withdraw electrons. Suitable examples include, but are notlimited to, a halo, cyano, fluoroalkyl, perfluoroalkyl, carboxy,alkoxycarbonyl, aryloxycarbonyl, halocarbonyl, formyl, carbonyl, sulfo,alkoxysulfonyl, aryloxysulfonyl, perfluoroalkylsulfonyl, alkylsulfonyl,azo, alkenyl, alkynyl, dialkylphosphonato, diarylphosphonato,aminocarbonyl, or combinations thereof.

As used herein, the term “fluoroalkyl” refers to an alkyl group that hasat least one hydrogen atom replaced with a fluorine atom.

As used herein, the term “formyl” refers to a monovalent group offormula —(CO)H where the carbon is attached to the oxygen atom with adouble bond.

As used herein, the term “halo” refers to a halogen group (i.e., F, Cl,Br, or I). In some embodiments, the halo group is F or Cl.

As used herein, the term “halocarbonyl” refers to a monovalent group offormula —(CO) X where X is a halogen group (i.e., F, Cl, Br, or I).

As used herein, the term “heteroaryl” refers to a monovalent radicalhaving a five to seven member aromatic ring that includes one or moreheteroatoms independently selected from S, O, N, or combinations thereofin the ring. Such a heteroaryl ring can be connected to or fused to upto five ring structures that are aromatic, aliphatic, or combinationsthereof. Examples of heteroaryl groups include, but are not limited to,quinolinyl, isoquinolinyl, quinazolinyl, quinoxalinyl, cinnolinyl,benzofuranyl, benzomercaptophenyl, benzoxazolyl, benzothiazolyl,benzimidazolyl, indolyl, phthalazinyl, benzothiadiazolyl,benzotriazinyl, phenazinyl, phenanthridinyl, acridinyl, and indazolyl,and the like. A heteroaryl is a subset of a heterocyclic group.

As used herein, the term “heterocyclic” refers to a monovalent radicalhaving a ring structure that is saturated or unsaturated and thatincludes one or more heteroatoms independently selected from S, O, N, orcombinations thereof in the ring. The heterocyclic group can be a singlering, bicyclic, or can be fused to another cyclic or bicyclic group. Thefused cyclic or bicyclic group can be saturated or unsaturated and canbe carbocyclic or contain heteroatoms.

As used herein, the term “hydroxy” refers to a group of formula —OH.

As used herein, the term “mercapto” refers to a group of formula —SH.

As used herein, the term “perfluoroalkyl” refers to an alkyl group thathas all the hydrogen atoms replaced with fluorine atoms. Aperfluoroalkyl is a subset of a fluoroalkyl.

As used herein, the term “perfluoroalkylsulfonyl” refers to a monovalentgroup of formula —SO₂R_(f) where R_(f) is a perfluoroalkyl.

As used herein, the term “polymerization” refers to forming a higherweight material from monomer or oligomers. The polymerization reactionalso can involve a cross-linking reaction.

As used herein when referring to a composition containing an initiatorsystem and polymerizable material, the term “shelf-stable” means thatthe composition can be stored for at least one day without any visiblegel formation at room temperature (i.e., 20° C. to 25° C.).

As used herein when referring to a compound, the term “oxidativestability” refers to the length of time needed to oxidize 50 weightpercent of the compound (t_(1/2)) at room temperature (i.e., 20° C. to25° C.) which can be calculated using pseudo-first order kinetics asdescribed in K. A. Connors, Chemical Kinetics: The Study of ReactionRates in Solution, Chapter 2, VCH, New York, 1990.

As used herein, the term “sulfo” refers to a group having the formula—SO₃H.

Compositions

A variety of materials are known for use as an electron donor ininitiator systems for polymerization reactions. However, some of thesematerials have limited solubility in ethylenically unsaturated monomers.Further, some of these materials have limited oxidative stability,shelf-stability, or combinations thereof.

One aspect of the invention provides a composition that includes anelectron donor and a sensitizing compound. More specifically, theelectron donor includes an arylsulfinate salt. The compositions can beused as photoinitiator systems for free radical polymerizationreactions.

The electron donor has an oxidation potential in N,N-dimethylformamideof 0.0 to +0.4 volts versus a silver/silver nitrate reference electrodeand is an arylsulfinate salt having an anion of Formula I

and having a cation that contains at least one carbon atom and either apositively charged nitrogen atom or a positively charged phosphorusatom. The Ar¹ group in Formula I is a substituted phenyl, anunsubstituted or substituted C₇₋₃₀ aryl, or an unsubstituted orsubstituted C₃₋₃₀ heteroaryl. A substituted Ar¹ group can have asubstituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group.

The electron donor is selected to have an oxidation potential in astated range. The oxidation potential can be determined using cyclicvoltammetry. As described herein, the oxidation potential is measured bydissolving the compound of interest in a non-aqueous solvent (i.e.,N,N-dimethylformamide) containing a supporting electrolyte (i.e., 0.1moles/liter tetrabutylammonium hexafluorophosphate). The resultingsolution is purged with an inert gas such as argon. A three-electrodeconfiguration is used that includes a working electrode (i.e., a glassycarbon electrode), a reference electrode (i.e., a silver wire in a 0.01moles/liter of silver nitrate dissolved in acetonitrile), and a counterelectrode (i.e., a platinum wire). The oxidation or reduction potentialis the voltage corresponding to the maximum current for the oxidationreaction.

One component of the composition is the electron donor. The electrondonor is an arylsulfinate salt having an anion of Formula I

and having a cation that contains at least one carbon atom and either apositively charged nitrogen atom or a positively charged phosphorusatom. The Ar¹ group in Formula I is a substituted phenyl, anunsubstituted or substituted C₇₋₃₀ aryl, or an unsubstituted orsubstituted C₃₋₃₀ heteroaryl. A substituted Ar¹ group can have asubstituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group. Thearylsulfinate salt is typically soluble in monomers capable ofundergoing free radical polymerization reactions and in a variety ofnon-polar and polar solvents. As used herein, the term “soluble” refersto a compound that can be dissolved in an amount at least equal to 0.05moles/liter, at least 0.07 moles/liter, at least 0.08 moles/liter, atleast 0.09 moles/liter, or at least equal to 0.1 moles/liter in a givenmaterial such as a solvent or monomer.

In some arylsulfinate salts, the Ar¹ group is a substituted phenyl or anunsubstituted or substituted C₇₋₃₀ aryl group having a carbocyclicaromatic ring. The aryl group can have a single carbocyclic aromaticring or can have additional carbocyclic rings that are fused orconnected to the carbocyclic aromatic ring. Any fused or connected ringscan be saturated or unsaturated. The aryl often contains up to 5 rings,up to 4 rings, up to 3 rings, up to 2 rings, or one ring. The aryl groupusually has up to 30 carbon atoms, up to 24 carbon atoms, up to 18carbon atoms, up to 12 carbon atoms, or 6 carbon atoms. Examples of arylgroups having a single ring or multiple fused rings include, but are notlimited to, phenyl, anthryl, naphthyl, acenaphthyl, phenanthryl,phenanthrenyl, perylenyl, and anthracenyl. A single bond, methylenegroup (i.e., —C(R^(b))₂— where each R^(b) is independently hydrogen,aryl, or alkyl), carbonyl group (i.e., —(CO)—), or combinations thereofcan connect multiple rings. Examples of aryl groups having multipleconnected rings include, but are not limited to, anthraquinonyl,anthronyl, biphenyl, terphenyl, 9,10-dihydroanthracenyl, and fluorenyl.

In other arylsulfinate salts, the Ar¹ group in Formula I can be anunsubstituted or substituted heteroaryl that has a five to seven memberaromatic ring that contains one or more heteroatoms independentlyselected from S, O, N, or combinations thereof in the ring. Theheteroaryl can have a single ring or can have multiple rings connectedor fused together. Any additional connected or fused rings can becarbocyclic or contain a heteroatom and can be saturated or unsaturated.The heteroaryl group often has up to 5 rings, up to 4 rings, up to 3rings, up to 2 rings, or one ring. The heteroaryl typically contains upto 30 carbon atoms. In some embodiments, the heteroaryl contains up to20 carbon atoms, up to 10 carbon atoms, or up to 5 carbon atoms.Examples of heteroaryl groups include, but are not limited to,quinolinyl, isoquinolinyl, quinazolinyl, quinoxalinyl, cinnolinyl,benzofuranyl, benzomercaptophenyl, benzoxazolyl, benzothiazolyl,benzimidazolyl, indolyl, phthalazinyl, benzothiadiazolyl,benzotriazinyl, phenazinyl, phenanthridinyl, acridinyl,azaphenanthrenyl, and indazolyl.

The Ar¹ group in Formula I can be substituted with an electronwithdrawing group or an electron withdrawing group in combination withan electron donating group provided that the arylsulfinate salt has anoxidation potential in N,N-dimethylformamide of 0.0 to +0.4 volts versusa silver/silver nitrate reference electrode. Electron donating groupscan be selected, for example, from a primary amino, secondary amino,tertiary amino, hydroxy, alkoxy, aryloxy, alkyl, or combinationsthereof. Electron withdrawing groups can be selected, for example, froma halo, cyano, fluoroalkyl, perfluoroalkyl, carboxy, alkoxycarbonyl,aryloxycarbonyl, halocarbonyl, formyl, carbonyl, sulfo, alkoxysulfonyl,aryloxysulfonyl, perfluoroalkylsulfonyl, alkylsulfonyl, azo, alkenyl,alkynyl, dialkylphosphonato, diarylphosphonato, aminocarbonyl, orcombinations thereof.

In some embodiments, the Ar¹ group includes an electron withdrawinggroup that is conjugated to the sulfinate group. For example, the Ar¹group can be a phenyl substituted with an electron withdrawing groupselected from halo, cyano, fluoroalkyl, perfluoroalkyl, carboxy,alkoxycarbonyl, aryloxycarbonyl, halocarbonyl, formyl, carbonyl, sulfo,alkoxysulfonyl, aryloxysulfonyl, perfluoroalkylsulfonyl, alkylsulfonyl,azo, alkenyl, alkynyl, dialkylphosphonato, diarylphosphonato,aminocarbonyl, or combinations thereof.

Specific examples of the arylsulfinate anion of Formula I include, butare not limited to, 4-chlorobenzenesulfinate, 4-cyanobenzenesulfinate,4-ethoxycarbonylbenzenesulfinate, 4-trifluoromethylbenzenesulfinate,3-trifluoromethylbenzenesulfinate, 1-naphthalenesulfinate,2-naphthalenesulfinate, and 1-anthraquinonesulfinate.

The arylsulfinate salts have a cation with at least one carbon atom andeither a positively charged nitrogen atom or a positively chargedphosphorus atom. In one embodiment, the cation of the arylsulfinate isof Formula II

where R¹ is an alkyl or aryl and each R⁴ is independently a hydrogen,alkyl, or aryl. The R¹ and R⁴ groups can be unsubstituted orsubstituted. An alkyl group can be substituted with a hydroxy. An arylcan be substituted with an alkyl, hydroxy, or combinations thereof.

In some examples of Formula II, R¹ and each R⁴ group are independently aC₂₋₃₀ alkyl that is unsubstituted or substituted with a hydroxy. Forexample, R¹ and each R⁴ independently can be an alkyl group having up to20, up to 10, up to 8, up to 6, or up to 4 carbon atoms. The alkyl groupoften has at least 2, at least 3, at least 4, at least 6, or at least 8carbon atoms. The alkyl group can have 4 to 30, 8 to 30, 3 to 10, 4 to10, 4 to 8, or 4 to 6 carbon atoms in some compounds. In a specificexample, the cation of the arylsulfinate salt is a tetrabutylammoniumion.

In other examples of Formula II, R¹ and two R⁴ groups are eachindependently a C₂₋₃₀ alkyl that can be unsubstituted or substitutedwith a hydroxy. The remaining R⁴ group is hydrogen. In still otherexamples, R¹ and one R⁴ group are each independently a C₄₋₃₀ alkyl thatis unsubstituted or substituted with a hydroxy; and the two remaining R⁴groups are hydrogen. In yet other examples, R¹ is a C₈₋₃₀ alkyl that isunsubstituted or substituted with a hydroxy; and the R⁴ groups arehydrogen.

The R¹ group and each of the R⁴ groups in Formula II independently canbe an aryl group that is unsubstituted or substituted with an alkyl,hydroxy, or combinations thereof. An exemplary cation istetraphenylammonium ion. In another example, R¹ and one R⁴ areindependently an aryl group that is unsubstituted or substituted with analkyl, hydroxy, or combinations thereof, and the two remaining R⁴ groupsare hydrogen. An exemplary cation is diphenylammonium ion.

In other embodiments, the cation of the arylsulfinate salt is a ringstructure that includes a 4 to 12 member heterocyclic group with apositively charged nitrogen atom. The heterocyclic group can besaturated or unsaturated and can contain up to three heteroatomsselected from nitrogen, oxygen, sulfur, or combinations thereof (i.e.,there is one positively charged nitrogen atom and up to two otherheteroatoms selected from nitrogen, oxygen, sulfur, or combinationsthereof). The ring structure can be unsubstituted or have a substituentselected from an alkyl, aryl, acyl, alkoxy, aryloxy, halo, mercapto,amino, hydroxy, azo, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl,halocarbonyl, or combinations thereof.

The heterocyclic group in the cationic ring structure can be a singlering, bicyclic, or can be fused to another cyclic or bicyclic group. Thefused cyclic or bicyclic group can be saturated or unsaturated and canhave 0 to 3 heteroatoms. The ring structure can include up to 30 carbonatoms, up to 24 carbon atoms, up to 18 carbon atoms, up to 12 carbonatoms, up to 6 carbon atoms, or up to 4 carbon atoms and up to 6heteroatoms, up to 4 heteroatoms, up to 2 heteroatoms, or 1 heteroatom.In some embodiments, the ring structure is a 4 to 12 member heterocyclicgroup that is a fused to an aromatic ring having 0 to 3 heteroatoms. Theheterocyclic group is bicyclic in some examples.

Suitable examples of five member heterocyclic groups that contain apositively charged nitrogen atom include, but are not limited to, apyrrolium ion, pyrazolium ion, pyrrolidinium ion, imidazolium ion,triazolium ion, isoxazolium ion, oxazolium ion, thiazolium ion,isothiazolium ion, oxadiazolium ion, oxatriazolium ion, dioxazolium ion,and oxathiazolium ion. These ions can be unsubstituted or substitutedwith an alkyl, aryl, acyl, alkoxy, aryloxy, halo, mercapto, amino,hydroxy, azo, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl,halocarbonyl group, or combinations thereof. In some applications, thecation is an imidazolium ion or oxazolium ion that is unsubstituted orsubstituted.

The five member heterocyclic groups can be fused to another cyclicgroup. In some exemplary ring structures, a five membered heterocyclicgroup is fused to an aromatic group. Exemplary ring structures include,but are not limited to, an indole ion, indazolium ion,benzopyrrolidinium ion, benzimidazolium ion, benzotriazolium ion,benzisoxazolium ion, benzoxazolium ion, benzothiazolium ion,benzisothiazolium ion, benzoxadiazolium ion, benzoxatriazolium ion,benzodioxazolium ion, benzoxathiazolium ion, carbozolium ion, andpurinium ion. These ions can be unsubstituted or substituted with analkyl, aryl, acyl, alkoxy, aryloxy, halo, mercapto, amino, hydroxy, azo,cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonyl group, orcombinations thereof. In some applications, the cation is abenzoxazolium ion or a benzothiazolium ion that is unsubstituted orsubstituted.

Suitable examples of six member heterocyclic groups that contain apositively charged nitrogen atom include, but are not limited to, apyridinium ion, pyridazinium ion, pyrimidinium ion, pyrazinium ion,piperazinium ion, triazinium ion, oxazinium ion, piperidinium ion,oxathiazinium ion, oxadiazinium ion, and morpholinium ion. These ionscan be unsubstituted or substituted with an alkyl, aryl, acyl, alkoxy,aryloxy, halo, mercapto, amino, hydroxy, azo, cyano, or carboxy,alkoxycarbonyl, aryloxycarbonyl, halocarbonyl group, or combinationsthereof. In some applications, the cation is a pyridinium ion or amorpholinium ion that is unsubstituted or substituted.

The six member heterocyclic groups can be fused to another cyclic group.In some exemplary ring structures, a six membered heterocyclic group isfused to an aromatic group. Exemplary ring structures include, but arenot limited to, isoquinolinium ion, quinolinium ion, cinnolinium ion,quinazolinium ion, benzopyrazinium ion, benzopiperazinium ion,benzotriazinium ion, benzoxazinium ion, benzopiperidinium ion,benzoxathiazinium ion, benzoxadizinium ion, benzomorpholinium ion,naphtyridinium ion, and acridinium ion. These ions can be unsubstitutedor substituted with an alkyl, aryl, acyl, alkoxy, aryloxy, halo,mercapto, amino, hydroxy, azo, cyano, or carboxy, alkoxycarbonyl,aryloxycarbonyl, halocarbonyl group, or combinations thereof.

Suitable examples of seven member heterocyclic groups that contain apositively charged nitrogen atom include, for example, an azepinium ionand diazepinium ion. These ions can be unsubstituted or substituted withan alkyl, aryl, acyl, alkoxy, aryloxy, halo, mercapto, amino, hydroxy,azo, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonylgroup, or combinations thereof.

Examples of heterocyclic groups that are bicyclic include, but are notlimited to, N-alkylated or N-protonated 1,4-diazabicyclo [2.2.2] octaneand N-alkylated or N-protonated 1-azabicyclic [2.2.2] octane that isunsubstituted or substituted with an alkyl, aryl, acyl, alkoxy, aryloxy,halo, mercapto, amino, hydroxy, azo, cyano, carboxy, alkoxycarbonyl,aryloxycarbonyl, halocarbonyl group, or combinations thereof.

In other embodiments, the cation of the arylsulfinate salt contains apositively charged phosphorus atom of Formula III

where each R² is independently an alkyl or aryl that is unsubstituted orsubstituted. An alkyl group can be substituted with a hydroxy. An arylcan be substituted with an alkyl, hydroxy, or combinations thereof.

In some examples of Formula III, all of the R² groups are an aryl group.For example, the cation can be a tetraphenylphosphonium ion. In otherexamples, one, two, or three of the R² groups are an aryl with theremaining R² group or groups being a C₂₋₃₀ alkyl.

Some of the arylsulfinate salts can have an anion of Formula IV

and a cation that includes a positively charged nitrogen atom. InFormula IV, R³ can be in an ortho, para, or meta position of the benzenering and is an electron withdrawing group selected from halo, cyano,fluoroalkyl, perfluoroalkyl, carboxy, alkoxycarbonyl, aryloxycarbonyl,halocarbonyl, formyl, carbonyl, sulfo, alkoxysulfonyl, aryloxysulfonyl,perfluoroalkylsulfonyl, alkylsulfonyl, azo, alkenyl, alkynyl,dialkylphosphonato, diarylphosphonato, or aminocarbonyl. In somecompounds, R³ is selected from cyano, carboxy, alkoxycarbonyl,aryloxycarbonyl, halocarbonyl, formyl, carbonyl, sulfo, alkoxysulfonyl,aryloxysulfonyl, perfluoroalkylsulfonyl, or alkylsulfonyl. In othercompounds, R³ is a halo, cyano, or alkoxycarbonyl group.

Specific examples Formula IV where R³ is located in the para position ofthe phenyl ring include 4-cyanobenzenesulfinate,4-chlorobenzenesulfinate, 4-ethoxycarbonylbenzenesulfinate, and4-trifluoromethylbenzenesulfinate. A specific example of R³ located inthe meta position of the phenyl ring includes3-trifluoromethylbenzenesulfinate.

For some applications, the arylsulfinate salt includes an anion ofFormula IV and a cation that is a tetraalkyammonium ion. The alkylgroups of the tetraalkylammonium ion can be the same or different andtypically contain 2 to 30 carbon atoms. For example, the alkyl groupscan contain 4 to 30 carbon atoms, 8 to 30 carbon atoms, 3 to 10 carbonatoms, 4 to 10 carbon atoms, 4 to 8 carbon atoms, or 4 to 6 carbonatoms. Specific arylsulfinate salts include, but are not limited to,tetrabutylammonium 4-chlorobenzenesulfinate, tetrabutylammonium4-cyanobenzenesulfinate, tetrabutylammonium4-ethoxycarbonylbenzenesulfinate, tetrabutylammonium4-trifluoromethylbenzenesulfinate, and tetrabutylammonium3-trifluoromethylbenzenesulfinate.

Other specific examples of electron donors include, but are not limitedto, tetrabutylammonium 1-naphthalenesulfinate, tetrabutylammonium2-naphthalenesulfinate, and tetrabutylammonium 1-anthraquinonesulfinate,1-ethyl-3-methylimidazolium 4-cyanobenzenesulfinate,N,N-dimethylmorpholinium 4-cyanobenzenesulfinate,3-ethyl-2-methylbenxoxazolium 4-cyanobenzenesulfinate,1-methyl-4-aza-1-azoniabicyclo[2.2.2]octane 4-cyanobenzenesulfinate, andN-hexadecylpyridinium 4-cyanobenzenesulfinate.

Another component of the compositions is a sensitizing compound that iscapable of absorbing actinic radiation in the range of 250 to 1000nanometers. In some embodiments, the sensitizing compound can absorbactinic radiation in the range of 300 to 1000 nanometers, in the rangeof 350 to 1000 nanometers, in the range of 250 to 850 nanometers, in therange of 250 to 800 nanometers, in the range of 400 to 800 nanometers,in the range of 425 to 800 nanometers, or in the range of 450 to 800nanometers.

Suitable sensitizing compounds that are dyes include, but are notlimited to, ketones (e.g., monoketones and diketones), coumarin dyes(e.g., ketocoumarins such as Coumarin 153), xanthene dyes (e.g., RoseBengal and Rhodamine 6G), acridine dyes, thiazole dyes, thiazine dyes(e.g., Methylene Blue and Methylene Violet), oxazine dyes (e.g., BasicBlue 3 and Nile Blue Chloride), azine dyes (e.g., Methyl Orange),aminoketone dyes, porphyrins (e.g., porphyrazine), aromatic polycyclichydrocarbons, p-substituted aminostyryl ketone compounds, aminotriarylmethanes, cyanine dyes (e.g., the cyanine dye described in Biochemistry,12, 3315 (1974)), squarylium dyes, pyridinium dyes, benzopyrilium dyes,and triarylmethane (e.g., Malachite Green). In some applications, thesensitizing compounds include xanthenes, monoketones, diketones, orcombinations thereof. Other suitable sensitizing dyes are described inF. J. Green, The Sigma-Aldrich Handbook of Stains, Dyes, and Indicators,Aldrich Chemical Company, Inc., Milwaukee, Wis. (1990).

In some embodiments, the sensitizing compound is a xanthene dye such asfluorosceins, rhodamines, eosins, and pyronins.

Exemplary monoketones include 2,2-dihydroxybenzophenone,4,4-dihydroxybenzophenone, 2,4-dihydroxybenzophenone, di-2-pyridylketone, di-2-furanyl ketone, di-2-mercaptophenyl ketone, benzoin,fluorenone, chalcone, Michler's ketone, 2-fluoro-9-fluorenone,2-chloromercaptoxanthone, acetophenone, benzophenone, 1- or2-acetonaphthone, 9-acetylanthracene, 2-, 3-, or 9-acetylphenanthrene,4-acetylbiphyenyl, propiophenone, n-butyrophenone, valerophenone, 2-,3-, or 4-acetylpyridine, 3-acetylcoumarin, and the like.

Exemplary diketones include aralkyldiketones such as anthraquinone,phenanthrenequinone, o-, m-, and p-diacetylbenzene, 1,3-, 1,4-, 1,5-,1,6-, 1,7-, and 1-8 diacetylnaphthalene, 1,5-, 1,8-, and9,10-diacetylanthracene, and the like. Exemplary alpha-diketones include2,3-butanedione, 2,3-pentanedione, 2,3-hexanedione, 3,4-hexanedione,2,3-heptanedione, 3,4-heptanedione, 2,3-octanedione, 4,5-octanedione,benzil, 2,2′-, 3,3′-, and 4,4′-dihydroxybenzil, furil,di-3,3′-indolylethanedione, 2,3-bornanedione (camphorquinone), biacetyl,1,2-cyclohexanedione, 1,2-naphthaquinone, acenaphthaquinone, and thelike.

The dye can have a molar extinction coefficient up to about 150,0001-mole⁻¹cm⁻¹. In some applications, the dye has a molar extinctioncoefficient that is up to 85,000 1-mole⁻¹cm⁻¹, up to 70,000, up to50,000, up to 30,000, up to 10,000, or up to 5,000 1-mole⁻¹cm⁻¹.

For applications requiring deep cure (e.g., cure of highly filledcomposites such as dental composites or cure of a thick sample), asensitizing compound is typically selected that has an extinctioncoefficient less than 1000 1-mole⁻¹cm⁻¹. In some examples, theextinction coefficient at the wavelengths of actinic radiation used forphotopolymerization is less than 500 or less than 100 1-mole⁻¹cm⁻¹. Thealpha-diketones, for example, are sensitizing compounds that can be usedfor such applications.

The sensitizing compound also can be a pigment as described in U.S. Pat.Nos. 4,959,297 and 4,257,915, the disclosures of which are incorporateherein by reference in their entirety. Suitable inorganic pigmentsinclude, but are not limited to, titanium dioxide, strontium titanate,barium titanate, zinc oxide, zinc sulfide, zinc selenide, cadmiumsulfide, cadmium selenide, cadmium telluride, or combinations thereof.Suitable organic pigments include, but are not limited to,phthalocyanine blue (pigment blue 15), copper polychlorophthalocyaninegreen (pigment green 7), copper polybromochlorophthalocyanine (pigmentgreen 36), perylene scarlet (vat red 29), perylene vermillion (pigmentred 23), perylene maroon, perylene Bordeaux, perylene dianhydride(perylene red), and those described in “Pigments-Inorganic” and“Pigments-Organic” in Kirk-Othmer Encyclopedia of Chemical Technology,Third ed., Volume 17, pp. 788-817, John Wiley and Sons, New York, 1982.The organic pigments also can be semiconducting polymers as described byY. M. Paushkin et al., Organic Polymeric Semiconductors, John Wiley &Sons, New York, 1974 and by J. M. Pearson, Pure and Appl. Chem., 49,463-477 (1977).

The composition can further include monomers that can be polymerizedusing a free-radical polymerization reaction. The monomers typicallycontain at least one ethylenically-unsaturated double bond. Themonomers, for example, can be monoacrylates, diacrylates, polyacrylates,monomethacrylates, dimethacrylates, polymethacrylates, or combinationsthereof. The monomers can be unsubstituted or substituted with ahydroxy. Exemplary monomers include methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate,isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate, allylacrylate, glycerol acrylate, glycerol diacrylate, glycerol triacrylate,ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol diacrylate, 1,3-propanediol diacrylate,1,3-propanediol dimethacrylate, trimethylolpropane triacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexaacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, andtris-hydroxyethyl-isocyanurate trimethylacrylate. The monomers also canbe bis-acrylates and bis-methacrylates of polyethylene glycol having anaverage molecular weight (M_(n)) of 200 to 500; copolymerizable mixturesof acrylated monomers such as those described in U.S. Pat. No.4,652,274, incorporated herein by reference in its entirety; acrylatedmonomers such as those described in U.S. Pat. No. 4,642,126,incorporated herein by reference in its entirety; unsaturated amidessuch as methylene bis-arylamide, methylene bis-methacrylamide,1,6-hexamethylene bis-acrylamide, diethylene triamine tris-acrylamide,and beta-methacrylaminoethyl methacrylate; and vinyl monomers such asstyrene, diallyl phthalate, divinyl succinate, divinyl adipate, anddivinylphthalate. Mixtures of two or more monomers can be used, ifdesired.

The electron donor and the sensitizing compound can be present in anamount effective to enable free radical polymerization of theethylenically-unsaturated monomers. In some applications, the electrondonor can be present in an amount up to 4 weight percent, up to 3 weightpercent, up to 2 weight percent, up to 1 weight percent, or up to 0.5weight percent based on the weight of the monomers. For example, theelectron donor can be present in an amount of 0.1 to 4 weight percent,0.1 to 3 weight percent, 0.1 to 2 weight percent, or 0.5 to 1 weightpercent based on the weight of the monomers.

The sensitizing compound is often used in an amount up to 4 weightpercent based on the weight of the monomers. In some applications, thesensitizing compound is present in an amount up to 3 weight percent, upto 2 weight percent, up to 1 weight percent, up to 0.5 weight percentbased on the weight of the monomers. For example, the sensitizingcompound can be present in an amount of 5 ppm to 4 weight percent, 10ppm to 2 weight percent, 15 ppm to 1 weight percent, or 20 ppm to 0.5weight percent based on the weight of the monomers.

The compositions can contain a wide variety of additives depending onthe desired use of the polymerized material. Suitable additives includesolvents, diluents, resins, binders, plasticizers, inorganic and organicreinforcing or extending fillers, thixotropic agents, UV absorbers,medicaments, and the like.

The compositions are typically free of an electron acceptor such asmetal ions in an oxidized state, persulfates, peroxides, iodonium salts,hexaarylbisimidazoles, or combinations thereof.

In some embodiments, the components of the compositions can be selectedto provide a useful combination of cure speed, cure depth, and shelflife. Some compositions can cure well even when loaded with largeamounts of fillers. The compositions can be used to form foams, shapedarticles, adhesives, filled or reinforced composites, abrasives,caulking and sealing formulations, casting and molding formulations,potting and encapsulating formulations, impregnating and coatingformulations, and the like.

Suitable applications for the compositions include, but are not limitedto, graphic arts imaging (e.g., for color proofing systems, curableinks, and silverless imaging), printing plates (e.g., for projectionplates and laser plates), photoresists, solder masks for printed circuitboards, coated abrasives, magnetic media, photocurable adhesives (e.g.,for orthodontics and general bonding applications), photocurablecomposites (e.g., for autobody repair and dental restoratives),protective coatings, and abrasion resistant coatings. The compositionsare also suitable for use in a multi-photon process, where highintensity/short pulse lasers are used in combination with suitable dyesand co-reactants to produce polymerizable compositions that are usefulfor imaging, microreplication and stereolithographic applications. Thecompositions can be used in other applications that are known to thoseskilled in the art.

Polymerization Methods

The invention also provides methods for photopolymerizing ethylenicallyunsaturated monomers using free radical polymerization reactions. Thephotopolymerization method includes irradiating a photopolymerizablecomposition with actinic radiation until the photopolymerizablecomposition gels or hardens. The photopolymerizable composition includesa photoinitiator system and monomers capable of undergoing free radicalpolymerization reactions (i.e., ethylenically unsaturated monomers). Thephotoinitiator system includes an electron donor and a sensitizingcompound. In some embodiments of the photopolymerizable composition, thecomponents can be mixed together and stored for at least one day priorto use.

The electron donor in the photoinitiator system includes anarylsulfinate salt having an anion of Formula I

and having a cation that contains at least one carbon atom and either apositively charged nitrogen atom or a positively charged phosphorusatom. The Ar¹ group in Formula I is a substituted phenyl, anunsubstituted or substituted C₇₋₃₀ aryl, or an unsubstituted orsubstituted C₃₋₃₀ heteroaryl. A substituted Ar¹ group can have asubstituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group. Theelectron donor has an oxidation potential in N,N-dimethylformamide of0.0 to +0.4 volts versus a silver/silver nitrate reference electrode. Insome embodiments, the oxidization potential in N,N-dimethylformamide is+0.08 to +0.4 volts, +0.08 to +0.3 volts, or +0.08 to +0.2 volts versusa silver/silver nitrate reference electrode.

The photopolymerizable compositions can include a wide variety ofdifferent types of sensitizing compounds such as dyes, organic pigments,inorganic pigments, or combinations thereof. In some embodiments, thesensitizing compound can change colors indicating that the polymericmaterial has been cured. The color changes can be attributed to chemicalalterations to the sensitizing compound.

The photoinitiator system can be activated by exposing the sensitizingcompound to actinic radiation having a wavelength in the range of 250 to1000 nanometers. In some applications, the actinic radiation has awavelength in the range of 300 to 1000 nanometers, in the range of 350to 1000 nanometers, in the range of 250 to 850 nanometers, in the rangeof 250 to 800 nanometers, in the range of 400 to 800 nanometers, in therange of 425 to 800 nanometers, or in the range of 450 to 800nanometers. An excited sensitizing compound is formed upon exposure tothe actinic radiation. The electron donor can donate an electron to theexcited sensitizing compound. The sensitizing compound is reduced andthe electron donor is oxidized. The oxidized electron donor is a radicalspecies that can function as an initiating free radical for thepolymerization reaction.

Monomers suitable for photopolymerization methods typically include anethylenically unsaturated monomer such as a monoacrylate,monomethacrylate, diacrylate, dimethacrylate, polyacrylate,polymethacrylate, or combinations thereof.

In some embodiments, visible light can be used to excite the sensitizingcompound and activate the photopolymerizable composition. This can beadvantageous because relatively inexpensive light sources can be used.Light sources emitting in the visible region of the electromagneticspectrum tend to be less expensive than those emitting, for example, inthe ultraviolet region. Other light sources that include ultravioletradiation or a combination of ultraviolet and visible radiation also canbe used. Typical light sources include, but are not limited to, mercuryvapor discharge lamps, carbon arcs, tungsten lamps, xenon lamps,sunlight, lasers, light emitting diodes, and the like.

Arylsulfinate Compounds

Another aspect of the invention provides arylsulfinate salts. In oneembodiment, the arylsulfinate salts have an anion of Formula I

where Ar¹ is a substituted phenyl, an unsubstituted or substituted C₇₋₃₀aryl, or an unsubstituted or substituted C₃₋₃₀ heteroaryl. A substitutedAr¹ group can have a substituent that is an electron withdrawing groupor an electron withdrawing group in combination with an electrondonating group. The cation of the arylsulfinate salt is of Formula II

where R¹ is independently an alkyl or aryl and each R⁴ is independentlyhydrogen, alkyl, or aryl. The R¹ and R⁴ groups can be unsubstituted orsubstituted. An alkyl group can be substituted with a hydroxy. An arylgroup can be substituted with a hydroxy, alkyl, or combinations thereof.

In other examples of Formula II, R¹ and two R⁴ groups are eachindependently a C₂₋₃₀ alkyl that can be unsubstituted or substitutedwith a hydroxy. The remaining R⁴ group is hydrogen. In still otherexamples, R¹ and one R⁴ group are each independently a C₄₋₃₀ alkyl thatis unsubstituted or substituted with a hydroxy; and the two remaining R⁴groups are hydrogen. In yet other examples, R¹ is a C₈₋₃₀ alkyl that isunsubstituted or substituted with a hydroxy; and the R⁴ groups arehydrogen.

In other examples of Formula II, R¹ and at least some of the R⁴ groupsinclude an aryl group such as a phenyl group. An exemplary cation istetraphenylammonium ion.

Some specific arylsulfinate salts that include an anion of Formula I anda cation of Formula II include, but are not limited to,tetrabutylammonium 1-naphthalenesulfinate, tetrabutylammonium2-naphthalenesulfinate, and tetrabutylammonium 1-anthraquinonesulfinate.

The arylsulfinate salt can have an anion of Formula IV

where R³ can be on an ortho, para, or meta position of the benzene ring.The R³ group is an electron withdrawing group selected from halo, cyano,fluoroalkyl, perfluoroalkyl, carboxy, alkoxycarbonyl, aryloxycarbonyl,halocarbonyl, formyl, carbonyl, sulfo, alkoxysulfonyl, aryloxysulfonyl,perfluoroalkylsulfonyl, alkylsulfonyl, or combinations thereof. Thechoice and location of the electron withdrawing group on the ring canaffect the oxidation potential of the arylsulfinate salt. Specificexamples of cations of Formula IV include 4-cyanobenzenesulfinate,4-chlorobenzenesulfinate, 4-ethoxycarbonylbenzenesulfinate,4-trifluoromethylbenzenesulfinate, and3-trifluoromethylbenzenesulfinate.

For some applications, the arylsulfinate salt includes an anion ofFormula IV and a cation that is a tetraalkylammonium ion. The alkylgroups can be the same or different and typically contains 1 to 10carbon atoms. For example, the alkyl groups can contain 3 to 10 carbonatoms, 4 to 10 carbon atoms, 4 to 8 carbon atoms, or 4 to 6 carbonatoms. Specific arylsulfinate salts include but are not limited to,tetrabutylammonium 4-chlorobenzenesulfinate, tetrabutylammonium4-cyanobenzenesulfinate, tetrabutylammonium4-ethoxycarbonylbenzenesulfinate, tetrabutylammonium4-trifluoromethylbenzenesulfinate, and tetrabutylammonium3-trifluoromethylbenzenesulfinate.

In other embodiments of an arylsulfinate salt, the anion is of Formula I

as described above and the cation is a ring structure that includes a 4to 12 member heterocyclic group having a positively charged nitrogenatom. In addition to the positively charged nitrogen heteroatom, theheterocyclic ring contains at least one additional heteroatom selectedfrom nitrogen, oxygen, sulfur, or combinations thereof. The heterocyclicgroup can be saturated or unsaturated. The ring structure can beunsubstituted or have a substituent selected from an alkyl, aryl, acyl,alkoxy, aryloxy, halo, mercapto, amino, hydroxy, azo, cyano, carboxy,alkoxycarbonyl, aryloxycarbonyl, halocarbonyl group, or combinationsthereof.

In some embodiments of the cationic ring structure, the heterocyclicgroup is fused to a cyclic or bicyclic group that is saturated orunsaturated and that has 0 to 3 heteroatoms. For example, theheterocyclic group can be fused to an aromatic group having 0 to 3heteroatoms.

Suitable examples of five member heterocyclic groups that contain apositively charged nitrogen atom include, but are not limited to, apyrazolium ion, imidazolium ion, triazolium ion, isoxazolium ion,oxazolium ion, thiazolium ion, isothiazolium ion, oxadiazolium ion,oxatriazolium ion, dioxazolium ion, and oxathiazolium ion.

Examples of five member heterocyclic groups that have a fused cyclicgroup include, but are not limited to, an indazolium ion,benzimidazolium ion, benzotriazolium ion, benzisoxazolium ion,benzoxazolium ion, benzothiazolium ion, benzisothiazolium ion,benzoxadiazolium ion, benzoxatriazolium ion, benzodioxazolium ion,benzoxathiazolium ion, and purinium ion.

Suitable examples of six member heterocyclic groups that contain apositively charged nitrogen atom include, but are not limited to, apyridazinium ion, pyrimidinium ion, pyrazinium ion, piperazinium ion,triazinium ion, oxazinium ion, oxathiazinium ion, oxadiazinium ion, andmorpholinium ion.

Examples of six member heterocyclic groups that have a fused cyclicgroup include, but are not limited to, cinnolinium ion, quinazoliniumion, benzopyrazinium ion, benzopiperazinium ion, benzotriazinium ion,benzoxazinium ion, benzoxathiazinium ion, benzoxadizinium ion, andbenzomorpholinium ion.

Specific examples of arylsulfinate salts having an anion of Formula Iand a cation with a nitrogen containing ring structure include, but arenot limited to, 1-ethyl-3-methylimidazolium 4-methylbenzenesulfinate,morpholinium 4-cyanobenzenesulfinate, 3-ethyl-2-methylbenxoxazolium4-cyanobenzenesulfinate, and 1-Methyl-4-aza-1-azoniabicyclo[2.2.2]octane4-cyanobenzenesulfinate.

In other embodiments of an arylsulfinate salt, the anion is of Formula I

as described above and the cation is of Formula III

where each R² is independently an alkyl or aryl that is substituted orunsubstituted. An alkyl can be substituted with a hydroxy. An aryl canbe substituted with an alkyl, hydroxy, or combinations thereof.

In some examples of cations according to Formula III, each R² is an arylgroup such as phenyl. The cation can be an unsubstituted or substitutedtetraphenylphosphonium ion.

Exemplary arylsulfinates having an anion of Formula I and a cation ofFormula III include, but are not limited to, tetraphenylphosphonium4-cyanobenzenesulfinate.

The arylsulfinate salts typically have a solubility equal to or greaterthan 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1 moles/liter in a givenmaterial such as a solvent or monomer. Thus, the arylsulfinates are notlimited to applications that include aqueous formulations or aqueoussystems with a large amount (e.g., 30 to 70 weight percent) of acosolvent such as an alcohol.

The arylsulfinates can be used to polymerize monomers without the needof adding a solvent for the purpose of dissolving the arylsulfinates.For example, the arylsulfinates can be used to polymerize non-polarmonomers such as 1,6-hexanediol diacrylate, stearyl acrylate, laurylacrylate, and the like. The polymerization reaction can occur in theabsence of added solvents (i.e., the arylsulfinates are soluble in thesenon-polar monomers).

In some embodiments, the arylsulfinates can be stored as a neat compoundat room temperature without undergoing oxidative degradation. Forexample, some of the arylsulfinates can be stored for greater than oneday, greater than 2 days, greater than 1 week, greater than 2 weeks, orgreater than 1 month. The time required at room temperature (i.e., 20°C. to 25° C.) to oxidize 50 percent of the compound (t_(1/2)) can beused to compare the relative ease of oxidative degradation of variousarylsulfinates. The t_(1/2) is calculated based on pseudo-first orderkinetics as described in K. A. Connors, Chemical Kinetics: The Study ofReaction Rates in Solution, Chapter 2, VCH, New York, 1990.

The arylsulfinates disclosed herein, at least in some applications, haveimproved solubility in a variety of monomers, enhanced storagestability, or a combination thereof compared to arylsulfinates having acation selected, for example, from an alkali metal or alkaline earthmetal.

EXAMPLES

Unless otherwise noted, as used herein:

the solvents and reagents were or can be obtained from Aldrich ChemicalCo., Milwaukee, Wis. or may be synthesized by known methods;

electrochemical instrumentation for cyclic voltammetry was obtained fromPrinceton Applied Research, Oak Ridge, Tenn.;

N,N-dimethylformamide was obtained from EM Science, Gibbstown, N.J.;

4-(trifluoromethyl)benzenesulfonyl chloride was obtained from AlfaAesar, Ward Hill, Mass.;

the term “emim” refers to the 1-ethyl-3-methylimidazolium cation;

the term “4-HBA” refers to 4-hydroxybutyl acrylate;

the term “HEA” refers to 2-hydroxyethyl acrylate;

the term “HDDA” refers to 1,6-hexanediol diacrylate;

the term “EYB” refers to Erythrosin Yellowish blend, which is a mixtureof 90% Erythrosin B and 10% Eosin Y and which was obtained from AldrichChemical Co.;

the term “Cyanine 1” refers to3-methyl-2-[5-(3-methyl-2-benzothiazolinylidene)-1,3-pentadienyl]benzothiazoliumiodide and was prepared according to the general method disclosed inBiochemistry, Vol. 13, no. 42 (1974), pp. 3315-3330

Methods

Measurement of Oxidation Potentials

The electrochemical measurements of the exemplary arylsulfinates weremade using an EG&G PARC Model 175 Universal Programmer, interfaced to aPrinceton Applied Research Model 173 potentiostat/galvanostat fittedwith a Princeton Applied Research Model 179 Digital Coulometer and Model178 Electrometer. The signal was digitized using a Model DI-151R5Waveform Recording System (available from DATAQ Instruments, Inc.,Akron, Ohio) and then stored and analyzed on a Dell OptiPlex XM 590 pc.The scan rates were 100 mV/sec.

The electrochemical measurements were made using a three-electrodeconfiguration: a reference electrode, a working electrode, and a counterelectrode. The reference electrode was a fritted electrode (obtainedfrom Sargent Welch, Buffalo Grove, Ill.) that was filled with 0.01MAgNO₃ in acetonitrile and fitted with a silver wire 1 mm in diameter byapproximately 19 cm in length. The counter electrode was a platinum wire1.0 mm in diameter and approximately 16 cm long (overall length) formedinto a coil having a coil diameter of approximately 10 mm and a coillength of about 7.5 cm. The working electrode was a glassy carbonelectrode, approximately 3.5 mm in diameter (obtained from BAS, Inc.,West Lafayette, Ind.). The glassy carbon electrode was polished usingfirst a 3.0 micron aluminum oxide powder/deionized water slurry, then a0.3 micron alpha alumina powder/deionized water slurry. The polishingpowders were obtained from Buehler LTD, Evanston, Ill.

The cell was a 50 mL four neck round bottom flask. Each electrode wassealed in the flask using the appropriately sized rubber septum. Thefourth inlet was used to introduce an argon purge to remove oxygen andkeep atmospheric moisture out of the cell.

The supporting electrolyte was tetrabutylammonium hexafluorophosphate(TBA PF₆) (obtained from Southwestern Analytical Chemicals, Inc.,Austin, Tex.). The TBA PF₆ was dried overnight in a vacuum oven at80-90° C. before each experiment. The solvent was N,N-dimethylformamide(DMF), and it was used as received without further purification. Thesolvent was transferred to the electrochemical cell via syringe under anargon atmosphere to minimize atmospheric moisture uptake.

Electrochemical measurements were made by first preparing a 0.1 molarsolution of TBA PF₆ in DMF. This solution was added to the cell, whichcontained a small magnetic stir bar, as argon gas was flowing throughthe cell. After the reference and counter electrodes were connected tothe instrumentation, the working electrode was polished as describedabove and was then inserted into the cell. A background scan wasconducted before the exemplary compounds were added to the cell. Then,approximately 10 mg of the compound was added to the cell and, after ithad dissolved, the measurement was made to record the oxidationpotential. The potential was determined at the peak current for theoxidation or reduction reaction on the first scan. In thisconfiguration, the oxidation potential of ferrocene in an identicalelectrolyte solution appeared at +0.1 volts versus the referenceelectrode.

Measurement of Oxidative Stability

The oxidative stability of the exemplary substituted arylsulfinates wasdetermined by proton nuclear magnetic resonance spectroscopy. Spectra ofsolutions of the compounds in acetonitrile-d₃ were obtained at regularintervals. The resonances of the alkyl groups in the cations were usedas an internal standard to assess the oxidation of the anion.

Preparative Example 1 Preparation of 4-Cyanobenzenesulfonyl Chloride

An intimate mixture of 4-carboxybenzenesulfonamide (188 g) and PCl₅ (430g) was made by combining the solids in a resealable plastic bag andmanually kneading and shaking the bag. The mixture was transferred to around bottom flask that was fitted with a magnetic stir bar and a hoseadapter that was connected to a source of nitrogen gas. The flask wasslowly heated to 60° C. in an oil bath and was held at 60° C. for 5hours as the mixture was stirred. The hose adapter was then connected toa water aspirator through a trap that was cooled with dry ice, and thetemperature of the oil bath was increased to 110° C. while the flask wasevacuated and liquid distilled into the trap. When the rate ofdistillation slowed, the hose adapter was again connected to thenitrogen source and the temperature of the oil bath was raised to 155°C. After an additional 13 hours, the hose adapter was again connected toa water aspirator through a trap and more liquid was distilled. Thereaction flask was then allowed to cool to room temperature, duringwhich time the brown product solidified. The crude product was vacuumdistilled, using a Kugelrhor distillation apparatus (available fromAldrich Chemical Co., Milwaukee, Wis.) at a temperature of 150° C. and apressure of 0.07 mmHg, into a collection bulb that was cooled in an icebath. The solid yellow distillate was washed from the collection bulbwith CH₂Cl₂ and that solution was concentrated to dryness with a rotaryevaporator to afford 167.4 g of product.

Preparative Example 2 Preparation of Potassium4-Ethoxycarbonylbenzenesulfonate

A mixture of sodium 4-carboxybenzenesulfonate (75 g) in deionized water(1200 mL) was heated to 60° C. until the solid was dissolved. Thissolution was passed through a column of a strongly acidic ion-exchangeresin (available under the trade designation AMBERLITE IR-120(PLUS) fromRohm and Haas Co., Philadelphia, Pa.) that had been acidified by washingsequentially with deionized water, concentrated aqueous HCl anddeionized water until the pH of the eluate was approximately 5.5. Thecolumn was then charged with the solution of sodium4-carboxybenzenesulfonate and was then washed with deionized water untila total of 2 L of eluate was collected. The deionized water was removedwith a rotary evaporator and the resultant intermediate was dried in avacuum oven overnight at 50° C.

The intermediate was then dissolved in anhydrous ethanol (1 L) in around bottom flask fitted with a magnetic stir bar, a condenser and ahose adapter that was attached to a source of nitrogen gas. Thissolution was stirred and heated overnight in an oil bath at 100° C. Anadditional 500 mL of ethanol was added to the flask and heating andstirring was continued for an additional 4 hours. The solution wasallowed to cool to room temperature and was neutralized with alcoholicKOH to the bromothymol blue endpoint. The product precipitated from thesolution and was isolated by vacuum filtration, washed with anhydrousethanol and dried overnight at room temperature to afford 75.1 g ofproduct.

Preparative Example 3 Preparation of 4-EthoxycarbonylbenzenesulfonylChloride

A round bottom flask, fitted with a magnetic stir bar and a hose adapterconnected to a source of nitrogen gas, was charged with a solution ofpotassium 4-ethoxycarbonylbenzenesulfonate (75.1 g) dissolved in a 3:1(v/v) mixture of acetonitrile (300 mL) and sulfolane (100 mL). As thesolution was stirred, POCl₃ (55 mL) was added slowly and the stirringmixture was heated at 75° C. under a nitrogen atmosphere for 3 hours.The heterogeneous reaction mixture was allowed to cool to roomtemperature and was then concentrated using a rotary evaporator. Theflask was then cooled in an ice bath and ice was added to the mixture inthe flask. The product crystallized as a white solid and was filteredand washed with cold deionized water. The product was dried under vacuumat room temperature and 3 mmHg for 2 hours to afford 76 g of whitesolid.

Preparative Example 4 Preparation of 1-Chlorosulfonylanthraquinone

Sodium anthraquinone-1-sulfonate (50.0 g) was combined with POCl₃ (31mL) and a 1:2 (v/v) mixture of sulfolane (100 mL) and acetonitrile (200mL). The mixture was stirred and heated to 110° C. under a nitrogenatmosphere for 44 hours. The mixture was allowed to cool to roomtemperature and was then further cooled in a refrigerator. The mixturewas filtered and the filtrate was poured onto ice in a beaker and thismixture was stirred for 1 hour. The brown precipitate was filtered,washed with deionized water, dried in air and then further driedovernight in a vacuum oven at 45° C. and less than 1 mmHg pressure togive 12.08 g of the product as a brown solid.

Preparative Examples 5-8 Preparation of Substituted Alkali MetalBenzenesulfinates

Substituted alkali metal benzenesulfinates were prepared by hydrolysisof the substituted benzenesulfonyl chlorides that were obtainedcommercially or were prepared as described in Preparative Examples 1 and3. Each substituted benzenesulfonyl chloride was stirred for 3 hours at75° C. in deionized water, at a concentration of 0.2 g of substitutedbenzenesulfonyl chloride per milliliter of deionized water, with 2.5equivalents of Na₂SO₃ and 2.5 equivalents of NaHCO₃ in a round bottomflask. Each reaction mixture was then allowed to cool to roomtemperature and was then cooled in a refrigerator to 10° C. Each coldsolution was acidified with concentrated sulfuric acid until the pH wasless than 1.

Each precipitated solid was extracted into ethyl acetate and then theorganic phase was evaporated to dryness using a rotary evaporator toafford the substituted benzenesulfinic acid as a colorless solid. Eachof the solid substituted benzenesulfinic acids was dissolved in methanolto give approximately 10 weight percent solutions. Deionized water wasthen added dropwise to each solution until a precipitate just formed.Sufficient methanol was then added to the solution until all of thesolid dissolved. Each aqueous methanol solution was neutralized with a1M aqueous solution of an alkali metal hydroxide (MOH), as indicated inTable 1, to afford the substituted alkali metal substitutedbenzenesulfinate salts, which were isolated by removal of the solventwith a rotary evaporator.

TABLE 1 Preparative Examples 5-8 Preparative Benzenesulfonyl Wt.Benzenesulfonyl Example chloride chloride MOH Wt. Benzenesulfinate 54-Cyano 11.68 g  NaOH 9.30 g 6 4-Ethoxycarbonyl 6.46 g LiOH 3.17 g 74-Chloro 5.11 g LiOH 3.06 g 8 4-Trifluoromethyl 6.20 g NaOH 4.15 g

Preparative Example 9 Preparation of N,N-Dimethylmorpholinium Hydroxide

To a stirred solution of N-methylmorpholine (10.0 g) in1,2-dichloroethane (125 mL) at room temperature there was added methyliodide (14.1 g). The colorless precipitate that formed was filtered andwas washed sequentially with 1,2-dichloroethane and petroleum ether. Thesolid was dried in air at room temperature to afford 21.3 g of product.A sample of this product (1.0 g) was dissolved in deionized water (2 mL)and was passed through a column of strongly basic ion-exchange resin(available under the trade designation DOWEX 1X2-100 from Dow ChemicalCo., Midland, Mich.) that had been washed sequentially with 10 g of a10% aqueous solution of NaOH and 200 mL of deionized water. The samplewas washed from the column with 25 mL of deionized water. The elutedsolution was concentrated to dryness using a rotary evaporator and wasfurther dried using a vacuum oven at 50° C. overnight to give theproduct as a colorless solid.

Preparative Example 10 Preparation of1-Methyl-4-aza-1-azoniabicyclo[2.2.2]octane Hydroxide

To a stirred solution of 1,4-diazabicyclo[2.2.2]octane (10.0 g) in1,2-dichloroethane (100 mL) at room temperature there was added methyliodide (12.7 g). The colorless precipitate that formed was filtered andwas washed sequentially with 1,2-dichloroethane and petroleum ether. Thesolid was dried in air at room temperature to afford 21.3 g of product.All of this product was then dissolved in deionized water (200 mL) andwas stirred at room temperature while ammonium hexafluorophosphate (13.7g) was slowly added to the solution. The colorless precipitate thatformed was vacuum filtered and was washed with a small amount ofdeionized water. The solid was allowed to dry in air at room temperatureovernight and was further dried using a vacuum oven at 60° C. overnightto afford 7.1 g of product. A sample of this product (1.0 g) wasdissolved in deionized water (2 mL) and was passed through a column ofstrongly basic ion-exchange resin (available under the trade designationDOWEX 1X2-100 from Dow Chemical Co., Midland, Mich.) that had beenwashed sequentially with 10 g of a 10% aqueous solution of NaOH and 200mL of deionized water. The sample was washed from the column with 25 mLof deionized water. The eluted solution was concentrated to drynessusing a rotary evaporator and was further dried using a vacuum oven at50° C. overnight to give the product as a colorless solid.

Preparative Example 11 Preparation of 3-Ethyl-2-methylbenzoxazoliumChloride

A solution of 3-ethyl-2-methylbenzoxazolium iodide (1.0 g) in deionizedwater (20 mL) was passed through a column of ion-exchange resin(available under the trade designation DOWEX 1X2-100 from Dow ChemicalCo., Midland, Mich.) that had been washed sequentially with deionizedwater (200 mL), saturated aqueous NaCl (50 mL), and deionized water (200mL). The product was washed from the column with approximately 50 mL ofdeionized water and was concentrated to dryness using a rotaryevaporator to afford 0.73 g of product.

Examples 1-4 Preparation of Substituted TetrabutylammoniumBenzenesulfinates

Substituted tetrabutylammonium benzenesulfinates were prepared from thecorresponding alkali metal sulfinates. Each alkali metal sulfinate wasdissolved in deionized water to give a 0.1M solution that was acidifiedwith concentrated sulfuric acid to afford the sulfinic acid as acolorless precipitate. Each mixture was extracted with ethyl acetate andthen the organic phase was evaporated to dryness using a rotaryevaporator. Each resultant solid was dissolved in 50% (v/v) aqueousmethanol and this solution was titrated with an aqueous solution oftetrabutylammonium hydroxide. Each mixture was evaporated to drynessusing a rotary evaporator to afford the product as a yellow oil. The ¹Hand ¹³C NMR spectra of each compound were consistent with the assignedstructure. Details of these preparations and oxidation and stabilitydata are given in Table 2.

TABLE 2 Examples 1-4 Example 1 2 3 4 Alkali Metal 4- 4-4-Trifluoromethyl 4- Benzenesulfinate Chloro Ethoxycarbonyl Cyano Wt.Alkali Metal 0.50 g 0.58 g 1.72 g 2.00 g Benzenesulfinate Wt. 0.98 g1.27 g 3.51 g 4.18 g Tetra- buylammonium Benzenesulfinate E_(ox) 0.09 V0.11 V 0.18 V 0.15 V t_(1/2) (days) 138 174 88 >300

Example 5 Preparation of emim 4-Methylbenzenesulfinate

A mixture of sodium 4-methylbenzenesulfinate (3.1 g) and anhydrousethanol (80 mL) in a round bottom flask, fitted with a magnetic stirbar, was heated to approximately 75° C. with stirring. The mixture wasallowed to cool to approximately 40° C. and then a solution of1-ethyl-3-methylimidazolium chloride (2.0 g) in anhydrous ethanol (20mL) was added to the flask. The mixture was stirred for 2 hours afterwhich time it was filtered. The filtrate was concentrated to drynessusing a rotary evaporator to give a heterogeneous yellow oil which wastaken up in CHCl₃. This mixture was filtered and then the filtrate wasconcentrated to dryness using a rotary evaporator to afford 3.12 g ofthe product as a yellow oil.

Example 6 Preparation of Tetraphenylphosphonium 4-Cyanobenzenesulfinate

A solution of sodium 4-cyanobenzenesulfinate (1.0 g) in anhydrousethanol (100 mL) was prepared in a 250 mL Erlenmeyer flask by heatingthe solution to boiling on a hot plate with magnetic stirring. To theboiling solution was added a hot solution of tetraphenylphosphoniumchloride (1.98 g) in anhydrous ethanol (50 mL) with constant stirring.The stirring solution was allowed to cool for 30 minutes, during whichtime a colorless precipitate appeared. The flask was then cooled in anice-bath for an additional 30 minutes with stirring. The mixture wasvacuum filtered and the filtrate was dried using a rotary evaporator toyield a deep yellow oil that contained some solid material. This residuewas dissolved in chloroform (50 mL) and the mixture was stirred for 20minutes and was then vacuum filtered. The deep yellow solution wasconcentrated to dryness using a rotary evaporator to afford a clearyellow oil that was further dried under vacuum for 1 hour at 3 mmHg toyield 2.20 g of the product as a bright yellow wax.

Example 7 Preparation of Tetrabutylammonium 1-Anthraquinone Sulfinate

A solution of 1-chlorosulfonylanthraquinone (12.05 g) was combined withdeionized water (200 mL), Na₂SO₃ (18.34 g) and NaHCO₃ (12.22 g) in around bottom flask. The mixture was stirred and heated under a nitrogenatmosphere at 65° C. for 2 hours. The solution was then allowed to coolto room temperature and was then further cooled in a refrigerator. Theprecipitated solid that formed was isolated by filtration and wasallowed to dry in air. The solid was transferred to a flask to which wasadded 200 mL of a 2:1 (v/v) mixture of methanol and deionized water. Thesolution was titrated with 40% aqueous tetrabutylammonium hydroxideuntil a deep red color persisted. The solvent was removed with a rotaryevaporator and the deep red oil was dried under high vacuum for 2 daysat 45° C. to afford 16.98 g of product.

Example 8 Preparation of Tetrabutylammonium 1-Naphthalene Sulfinate

A round bottom flask was charged with 1-naphthalenesulfonyl chloride(20.0 g), Na₂SO₃ (33.36 g), NaHCO₃ (22.24 g) and deionized water (350mL). The mixture was stirred and heated to 65° C. under a nitrogenatmosphere for 2 hours, after which time the mixture was allowed to coolto room temperature and was then further cooled in a refrigerator. Thecold mixture was acidified with concentrated H₂SO₄ which resulted in theformation of a precipitate. The mixture was extracted three times with100 mL of ethyl acetate. The organic extracts were combined and thesolvent was removed with a rotary evaporator to give a colorless solidthat was then dissolved in 240 mL of 1:1 (v/v) methanol-deionized waterin a beaker. The solution was titrated with a solution of 40% aqueoustetrabutylammonium hydroxide until the pH of the solution was 7.2. Thesolvent was removed with a rotary evaporator and the product was furtherdried in a vacuum oven at room temperature to afford 36.4 g of a yellowwaxy solid.

Example 9 Preparation of Tetrabutylammonium 2-Naphthalene Sulfinate

A round bottom flask was charged with 2-naphthalenesulfonyl chloride(24.73 g), Na₂SO₃ (41.25 g), NaHCO₃ (41.25 g) and 350 mL deionizedwater. The mixture was stirred and heated to 65° C. under a nitrogenatmosphere for 2 hours, after which time the mixture was allowed to coolto room temperature and was then further cooled in a refrigerator. Thecold mixture was acidified with concentrated H₂SO₄, which resulted inthe formation of a precipitate.

The mixture was extracted three times with 100 mL of ethyl acetate. Theorganic extracts were combined and the solvent was removed with a rotaryevaporator to give a colorless solid that was then dissolved in 240 mLof 1:1 (v/v) methanol-deionized water in a beaker. The solution wastitrated with a solution of 40% aqueous tetrabutylammonium hydroxideuntil the pH of the solution was 7.2. The solvent was removed with arotary evaporator and the product was further dried in a vacuum oven atroom temperature to afford 46.9 g of a yellow waxy solid.

Example 10 Preparation of N,N-Dimethylmorpholinium4-Cyanobenzenesulfinate

Concentrated sulfuric acid was slowly added to a solution of sodium4-cyanobenzenesulfinate (0.15 g) in deionized water (10 mL). Aprecipitate formed and sulfuric acid was added dropwise until itappeared that no more precipitate was forming. The mixture was extractedtwice with ethyl acetate (20 mL) and the combined organic phases wereconcentrated to dryness using a rotary evaporator. The resultant solidwas dissolved in 50 weight percent aqueous methanol and this solutionwas titrated with a solution of N,N-dimethylmorpholinium hydroxide (0.85g) in deionized water (5 mL). The solution was concentrated to drynessusing a rotary evaporator and was further dried using a vacuum oven atroom temperature overnight. The resultant solid was then dissolved indeionized water and this solution was extracted twice with ethyl acetate(20 mL). The combined organic phases were concentrated to dryness usinga rotary evaporator. The resultant solid was further dried using avacuum oven overnight at room temperature to afford 0.24 g of product asa yellow oil.

Example 11 Preparation of 1-Methyl-4-aza-1-azoniabicyclo[2.2.2]octane4-Cyanobenzenesulfinate

Concentrated sulfuric acid was slowly added to a solution of sodium4-cyanobenzenesulfinate (0.25 g) in deionized water (10 mL). Aprecipitate formed and sulfuric acid was added dropwise until itappeared that no more precipitate was forming. The mixture was extractedtwice with ethyl acetate (20 mL) and the combined organic phases wereconcentrated to dryness using a rotary evaporator. The resultant solidwas dissolved in 50 weight percent aqueous methanol and this solutionwas titrated with a solution of the product of Preparative Example 10(0.27 g) in deionized water (5 mL) to a pH of approximately 7.2. Thesolution was concentrated to dryness using a rotary evaporator and wasfurther dried using a vacuum oven at room temperature overnight toafford 0.45 g of product as a yellow waxy solid.

Example 12 Preparation of N-Hexadecylpyridinium 4-Cyanobenzenesulfinate

A solution of N-hexadecylpyridinium chloride (1.6 g) in ethanol (20 mL)was added to an Erlenmeyer flask containing a magnetically stirredboiling solution of sodium 4-cyanobenzenesulfinate (1.0 g) in anhydrousethanol (200 mL). The mixture was allowed to cool to room temperatureand was then further cooled in an ice bath. The mixture was filtered andthe filtrate was concentrated to dryness using a rotary evaporator. Theresidue was then dissolved in chloroform (100 mL), filtered, andconcentrated to dryness using a rotary evaporator to afford 2.4 g ofproduct.

Example 13 Preparation of 3-Ethyl-2-methylbenzoxazolium4-Cyanobenzenesulfinate

A solution of 3-ethyl-2-methylbenzoxazolium chloride (0.73 g) in ethanol(20 mL) was added to an Erlenmeyer flask containing a magneticallystirred boiling solution of sodium 4-cyanobenzenesulfinate (0.1 g) inanhydrous ethanol (20 mL). The mixture was allowed to cool to roomtemperature and was then further cooled in an ice bath. The mixture wasfiltered and the filtrate was concentrated to dryness using a rotaryevaporator. The residue was mixed with deionized water and this mixturewas extracted with ethyl acetate (2×20 mL). The combined organicextracts were concentrated to dryness using a rotary evaporator. Theresultant solid was then dissolved in methylene chloride, filtered andevaporated to dryness using a rotary evaporator to afford 0.08 g ofproduct.

Examples 14-17 Photocuring of HEA Using Tetrabutylammonium4-Cyanobenzenesulfinate

A stock solution of HEA and 1 weight percent tetrabutylammonium4-cyanobenzenesulfinate was prepared. Screw-cap vials were charged withapproximately 1 g of this solution. An amount of a dye was added to eachvial to give a dye concentration sufficient to provide a lightly coloredsolution, typically between 50 and 1000 ppm, depending on the dye. Eachsolution was purged with nitrogen gas for 30 seconds after which timethe vials were sealed. Each solution was irradiated with a 100 Wquartz-tungsten-halogen (QTH) light source (model I-100, available CudaFiberoptics, Jacksonville, Fla.) by holding and slowly agitating eachvial approximately 2 cm in front of the light source. The light sourceshutter was fully open. Cure time was considered to be the time that ittook for the solution to no longer flow in the vial as the vial wasagitated. The results are given in Table 3.

TABLE 3 Examples 14-17 Example Dye Cure Time (sec) 14 Methylene blue 1215 Basic Blue 3 28 16 Cyanine 1 150 17 Rose Bengal 360

Example 18 Photocuring of 4-HBA Using Tetrabutylammonium4-Cyanobenzenesulfinate and Methylene Green

A mixture of 4-HBA (0.5 g) with 1 weight percent of the product ofExample 4 was prepared. Methylene green was added in an amountsufficient to provide a lightly colored solution. The sample wasevaluated for rate and extent of cure by photo differential scanningcalorimetry (photo-DSC) using a model DSC2920 calorimeter (availablefrom TA Instruments, New Castle, Del.) with actinic radiation lower inenergy than 300 nm at an irradiance of 20 mW/cm². The results are givenin Table 4.

TABLE 4 Curing of Examples 18 Initial Slope Time to peak Total evolvedExample (W/g-min) maximum (min) heat (J/g) 18 26 0.14 380

Examples 19-22 Photocuring of HDDA Using Tetrabutylammonium ArylsufinateSalts and EYB

A mixture of HDDA (11.03 g) and EYB (0.056 g) in a glass vial wassonicated for five minutes using a laboratory sonication bath that wasfilled with water. The mixture was then filtered using 0.45 micronsyringe filter to give a pink solution which was then divided into nineweighed portions in separate screw cap glass vials. To each of four ofthe vials was added one of the tetrabutylammonium arylsulfinate saltsfrom Examples 2, 4, 8, and 9 in a quantity sufficient to give a 1 weightpercent mixture of the tetrabutylammonium arylsulfinate salt in the HDDAsolution. Each of these vials was sonicated for five minutes in asonication bath and then each mixture was purged with nitrogen gas fortwo minutes, after which time the vials were sealed. Each mixture wasirradiated with a 100 W quartz-tungsten-halogen (QTH) light source(model I-100, available Cuda Fiberoptics, Jacksonville, Fla.) by holdingand slowly agitating each vial approximately 2 cm in front of the lightsource. The light source shutter was fully open. Cure time wasconsidered to be the time that it took for the solution to no longerflow in the vial as the vial was agitated. The results are given inTable 5.

TABLE 5 Curing of Examples 19-22 Example Arylsulfinate salt from ExampleCure Time (sec) 19 2 30 20 4 22 21 8 7 22 9 5

Comparative Examples 1-4 Irradiation of HDDA Using Alkali MetalBenzenesulfinate Salts and EYB

To each of four of the remaining vials containing HDDA and EYB fromExamples 19-22 was added one alkali metal benzenesulfinate salt, asindicated in Table 6, in a quantity sufficient to give a 1 weightpercent mixture of the alkali metal arylsulfinate salt in the HDDAsolution. Each of these vials was sonicated for five minutes in asonication bath and then each mixture was purged with nitrogen gas fortwo minutes, after which time the vials were sealed. Each mixture wasirradiated with a 100 W quartz-tungsten-halogen (QTH) light source(model I-100, available Cuda Fiberoptics, Jacksonville, Fla.) by holdingand slowly agitating each vial approximately 2 cm in front of the lightsource. The light source shutter was fully open. Each vial wasirradiated for 90 seconds, after which time each of the mixtures wasobserved not to be cured.

TABLE 6 Substituted alkali metal benzenesulfinate salts ComparativeExample Substituted alkali metal benzenesulfinate salt 1 Lithium4-(trifluoromethyl)benzenesulfinate 2 Lithium 4-chlorobenzenesulfinate 3Sodium 4-cyanobenzenesulfinate 4 Lithium 4-carboethoxybenzenesulfinate

Comparative Example 5 Irradiation of a mixture of HDDA and EYB

The HDDA and EYB mixture in the remaining vial from Examples 19-22 waspurged with nitrogen gas for two minutes, after which time the vial wassealed. The mixture was irradiated with a 100 W quartz-tungsten-halogen(QTH) light source (model I-100, available Cuda Fiberoptics,Jacksonville, Fla.) by holding and slowly agitating the vialapproximately 2 cm in front of the light source. The light sourceshutter was fully open. The vial was irradiated for 90 seconds, afterwhich time the mixture was observed not to be cured.

1. An arylsulfinate salt comprising: an anion of Formula I

wherein Ar¹ is a substituted phenyl, an unsubstituted or substitutedC₇₋₃₀ aryl, or an unsubstituted or substituted C₃₋₃₀ heteroaryl, saidsubstituted Ar¹ having a substituent that is an electron withdrawinggroup or an electron withdrawing group in combination with an electrondonating group; and a cation comprising a ring structure comprising a 4to 12 member heterocyclic group with a positively charged nitrogen atomand at least one other heteroatom selected from nitrogen, oxygen,sulfur, or combinations thereof, said heterocyclic group being saturatedor unsaturated, wherein said ring structure can be unsubstituted orsubstituted with a substituent selected from an alkyl, aryl, acyl,alkoxy, aryloxy, halo, mercapto, amino, hydroxy, azo, cyano, carboxy,alkoxycarbonyl, aryloxycarbonyl, or halocarbonyl group.
 2. Thearylsulfinate salt of claim 1, wherein said heterocyclic group is fusedto a cyclic or bicyclic group that is saturated or unsaturated and thathas 0 to 3 heteroatoms.
 3. The arylsulfinate salt of claim 1, whereinthe heterocyclic group is a heterobicyclic group.
 4. The arylsulfinatesalt of claim 1, wherein the heterocyclic group is selected from apyrazolium ion, imidazolium ion, triazolium ion, isoxazolium ion,oxazolium ion, thiazolium ion, isothiazolium ion, oxadiazolium ion,oxatriazolium ion, dioxazolium ion, oxathiazolium ion, pyridazinium ion,pyrimidinium ion, pyrazinium ion, piperazinium ion, triazinium ion,oxazinium ion, oxathiazinium ion, oxadiazinium ion, or morpholinium ion.5. The arylsulfinate salt of claim 1, wherein the heterocyclic group isselected from an indazolium ion, benzimidazolium ion, benzotriazoliumion, benzisoxazolium ion, benzoxazolium ion, benzothiazolium ion,benzisothiazolium ion, benzoxadiazolium ion, benzoxatriazolium ion,benzodioxazolium ion, benzoxathiazolium ion, purinium ion, cinnoliniumion, quinazolinium ion, benzopyrazinium ion, benzopiperazinium ion,benzotriazinium ion, benzoxazinium ion, benzoxathiazinium ion,benzoxadizinium ion, or benzomorpholinium ion.
 6. The arylsulfinate saltof claim 1, wherein the Ar¹ group of the arylsulfinate salt is asubstituted phenyl, an unsubstituted or substituted naphthyl, or anunsubstituted or substituted anthraquinonyl, said substituted Ar¹ havinga substituent that is an electron withdrawing group or an electronwithdrawing group in combination with an electron donating group.
 7. Thearylsulfinate salt of claim 1, wherein the anion of the arylsulfinatesalt is a benzenesulfinate substituted with an electron withdrawinggroup electron selected from halo, cyano, fluoroalkyl, perfluoroalkyl,carboxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonyl, formyl,carbonyl, sulfo, alkoxysulfonyl, aryloxysulfonyl,perfluoroalkylsulfonyl, alkylsulfonyl, azo, alkenyl, alkynyl,dialkylphosphonato, diarylphosphonato, aminocarbonyl, or combinationsthereof.
 8. The arylsulfinate salt of claim 1, wherein the arylsulfinatesalt is N,N-dimethylmorpholinium 4-cyanobenzenesulfinate,1-methyl-4-aza-1-azoniabicyclo [2.2.2]octane 4-cyanobenzenesulfinate,3-ethyl-2-methylbenzoxazolium 4-cyanobenzenesulfinate,N-hexadecylpyridinium 4-cyanobenzenesulfinate, or combinations thereof.9. An arylsulfinate salt comprising: an anion of Formula I

wherein Ar¹ is a substituted phenyl, a substituted C₇₋₃₀ aryl, or anunsubstituted or substituted C₃₋₃₀ heteroaryl, said substituted Ar¹having a substituent that is an electron withdrawing group or anelectron withdrawing group in combination with an electron donatinggroup, wherein the electron withdrawing group electron is selected fromcyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonyl, formyl,carbonyl, sulfo, alkoxysulfonyl, aryloxysulfonyl,perfluoroalkylsulfonyl, alkylsulfonyl, azo, alkenyl, alkynyl,dialkylphosphonato, diarylphosphonato, aminocarbonyl, or combinationsthereof and a cation is of Formula III

where each R² is independently an unsubstituted alkyl, an alkylsubstituted with a hydroxy, an unsubstituted aryl, or an arylsubstituted with an alkyl, hydroxy, or combinations thereof.
 10. Thearylsulfinate salt of claim 9, wherein the compound istetraphenylphosphonium 4-cyanobenzenesulfinate.
 11. The arylsulfinatesalt of claim 9, wherein the Ar¹ group of the arylsulfinate salt is asubstituted phenyl, a substituted naphthyl, or an unsubstituted orsubstituted anthraquinonyl, said substituted Ar¹ having a substituentthat is an electron withdrawing group or an electron withdrawing groupin combination with an electron donating group.
 12. The arylsulfinatesalt of claim 9, wherein the anion of Formula I is4-cyanobenzenesulfinate.
 13. The arylsulfinate salt of claim 9, whereinthe anion of Formula I is 4-ethoxycarbonylbenzenesulfinate.
 14. Anarylsulfinate salt comprising: an anion of Formula I

wherein Ar¹ is a substituted phenyl, a substituted C₇₋₃₀ aryl, or asubstituted C₃₋₃₀ heteroaryl, said substituted Ar¹ having a substituentthat is an electron withdrawing group in combination with an electrondonating group, wherein the electron withdrawing group electron isselected from halo, fluoroalkyl, perfluoroalkyl, or combinations thereofand wherein the electron donating group is selected from a primaryamino, secondary amino, tertiary amino, hydroxy, alkoxy, aryloxyl, orcombinations thereof and a cation is of Formula III

where each R² is independently an unsubstituted alkyl, an alkylsubstituted with a hydroxy, an unsubstituted aryl, or an arylsubstituted with an alkyl, hydroxy, or combinations thereof.